1. Field of the Invention
This invention relates to a method of removing sulfur dioxide from sulfur dioxide-containing gas using as the absorbent, a slurry solution prepared by suspending in water minute particles of slags from furnaces, such as, blast furnaces, converters and open-hearth furnaces.
2. Description of the Prior Art
Generally, the slags from blast and open-hearth furnaces and converters are only partially utilized in the manufacture of cement, bricks, heat-resisting materials and the like. The greater part goes into reclamation work as ballast. These slags are formed when iron ore is heated to upwards of 1000.degree. C so that the impurities therein combine with lime and other additives in the molten state to form double salts. An X-ray analysis of blast furnace slag revealed the presence of Ca.sub.2 Al.sub.2 SiO.sub.7 as the principal component. This double salt is stable at normal temperature and is difficult to dissolve or dissociate in water. Table I shows a typical composition of blast furnace slag, indicating a calcium content of about 40% in terms of CaO. However, as noted, these materials are present primarily as the double salt.
Table 1 ______________________________________ Component Percentage (wt %) ______________________________________ SiO.sub.2 33.7 Fe.sub.2 O.sub.3 2.7 Al.sub.2 O.sub.3 15.9 TiO.sub.2 1.4 MnO 0.4 CaO 39.9 MgO 3.7 Others Remainder Total 100.0 ______________________________________
It is, of course, well known to use CaO as a principal reactant in the purification of SO.sub.2 -containing gases and to produce gypsum as a by-product of this process. Typically, this process involves the steps of crushing the CaO, suspending the resulting powder in water, and circulating the suspension at a pH of 6 to 7 in an absorbing tower in contact with the gas to thus absorb the SO.sub.2. The reactions for this process are as follows: EQU SO.sub.2 (g) .revreaction. SO.sub.2 (l) (1) EQU SO.sub.2 (l) + H.sub.2 O .revreaction. H.sub.2 SO.sub.3 ( 2) EQU ca(OH).sub.2 + H.sub.2 SO.sub.3 .fwdarw. CaSO.sub.3 + 2H.sub.2 O (3)
after dissolution in the water, the sulfur dioxide is hydrolyzed to produce H.sub.2 SO.sub.3 (equation 2). This then reacts with the Ca(OH).sub.2 in the water to produce CaSO.sub.3.
It should be noted that the calcium hydroxide is in solution in this process and thus is dissociated as follows: EQU Ca(OH).sub.2 .revreaction. Ca.sup.+ + 2OH.sup.- ( 4)
consequently, the solution is alkaline. However, the double salts from which the above mentioned slags are formed do not ionize in water or in H.sub.2 SO.sub.3 solution and consequently do not form the hydroxyl ion. Thus, these slags have not been used for SO.sub.2 removal processes since they do not provide a good absorbent for SO.sub.2.